Chemo-mechanical grinding by applying grain boundary cohesion fixed abrasive for monocrystal sapphire

This paper presents a novel fixed abrasive tool namely grain boundary cohesion fixed abrasive pellet (GBCFAP) which is able to provide higher finishing efficiency as well as better surface/subsurface quality of sapphire substrate during the chemo-mechanical grinding (CMG) process. The manufacturing procedures of GBCFAP are introduced in detail in this paper. It is found that the sintering temperature plays an important role to the strength of GBCFAP, and the strength of GBFCAP could be flexibly adjusted by sintering temperature. The experiment result suggests that the recommended sintering temperature ranges from 600 to 650 °C according to current CMG conditions. Meanwhile, comparing with conventional resin bound CMG wheel, 600 °C sintered GBCFAP CMG wheel performs better in terms of material removal rate and surface/subsurface quality since the chemical effect and mechanical effect during CMG process are well balanced. Meanwhile, the solid phase reaction between sapphire and Cr₂O₃ abrasive is demonstrated by TEM observation and XPS quantification.     

球形磁性磨料磁力研磨ZrO2材料机理研究

在磁力研磨加工ZrO 2材料过程中,分析了单颗磁性磨料在加工区域内的受力情况,并对研磨压力的形成进行探讨,利用公式推导计算研磨压力,通过研磨压力的大小分析了磁力光整加工中材料的去除机理,包括脆性断裂去除、塑性变形去除和粉末化去除。通过白光干涉仪、扫描电子显微镜等分析检测仪器对磁力研磨加工后的工件表面进行检测,可知在其他条件相同时,磁力研磨加工后的工件材料精度高于传统的草轮抛光精度,可达到0.59μm。     

固着磨料加工碳化硅反射镜的初步实验研究

本文采用了一种有别于传统的加工碳化硅反射镜的工艺---固着磨料加工工艺。此工艺不但可以利用大颗粒金刚石磨料快速加工出较好的镜面质量,而且由于其固着磨料与工件相对运动关系固定,有利于精确加工。在工艺实验中,分别测得了W7,W5,W3.5,W1.5固着磨料丸片在特定转速和压力下对碳化硅材料的去除特性。通过多组去除量曲线,我们得出此工艺不仅有着较高的去除率,而且其稳定性非常良好。另外在表面粗糙度结果方面,最初使用W7丸片获得了粗糙度为42.758nm rms的镜面。我们不断减小所用丸片的粒度,工件表面粗糙度随之减小。在使用W1.5丸片抛光后,最终获得了粗糙度为1.591nm rms的光滑镜面。实验结果表明,固着磨料加工碳化硅反射镜工艺在某些加工阶段内可以取代传统的散粒磨料加工工艺,有着良好的应用前景。     

Development of a new magnetic abrasive finishing process with renewable abrasive particles using the circulatory system

In order to improve the finishing efficiency of the Magnetic Abrasive Finishing process, we proposed a new MAF process with renewable abrasive particles using compound magnetic finishing fluid circulatory system in this paper. This new finishing process has a circulating system that uses a conveyor belt to renew the mixed abrasive particles. This not only maintains the stability of the finishing but also ensures that the processing does not need to be interrupted. In this study, we investigated the magnetic field distribution, finishing force, and finishing behavior of the processing area. Furthermore, we designed experimental device to finish the sus304 stainless steel plate, to verify the feasibility of this process and understand its characteristics through processing experiments. Moreover, the influence of important process parameters, including magnetic particles, abrasive particles, conveyor belt line speed and working gap, on the surface quality of the workpiece is studied through the experiment. The experimental results indicate that the present process can achieve stable processing of the material surface without interruption, and the surface roughness of the sus304 stainless steel plate has been improved from 273 nm to 23 nm through this process.     

Effects of finishing in abrasive fluid machining on microholes fabricated by EDM

This research investigated the effects of the fine-finishing process on microholes in abrasive fluid machining (AFM). Microholes on stainless steel (SUS 304) and titanium alloy (Ti-6Al-4V) plates were fabricated using a deep drilling machine of electrical discharge machining (EDM) prior to AFM. In the experiment, the Taguchi method was adopted to explore the effects of the machining parameters associated with AFM on the experimentally observed values, such as the material removal rate (MRR) and differences between the dimensions of the entrance and the exit of the microhole. Furthermore, the improvement in the shape precision of the microhole fabricated by EDM and subsequently fine-finished by AFM was also elucidated by using a scanning electron microscope (SEM). The significant machining parameters and the optimal combination levels of the machining parameters were identified by analysis of variance (ANOVA) and the S/N (signal-to-noise) ratio response graph obtained from the analysis of the experimental data.     

固着磨料加工碳化硅反射镜的材料去除率及表面粗糙度的理论研究

本文基于固着磨料加工碳化硅反射镜的微观作用原理，理论上定量分析探讨了金刚石磨料压入碳化硅工件的深度对材料去除率、光学元件表面粗糙度的影响，分别获得了材料去除率数学模型及粗糙度的仿真计算结果。通过去除率及粗糙度的实验与理论模型的对比结果来看，实验值虽与理论值有偏差，但基本稳定在同一数量级内，由此验证了理论分析的正确性。固着磨料工艺的这一易于理论预测的特性对实际的光学加工有着极为重要的意义，因此这种较为新颖的固着磨料工艺在碳化硅反射镜加工领域内有着广阔的应用前景。     

Electrical discharge abrasive drilling of hard materials using a metal matrix composite electrode

The main object of the present work was to develop an electrical discharge abrasive drilling (EDAD) methodology to remove the re-solidified layer through the grinding induced by a metal matrix composite electrode prior to the re-solidification of molten material. A metal matrix composite (Cu/SiC_p) electrode, with an electroless pretreatment of Cu coating on SiC_p to enhance bonding status between Cu and SiC_p, was made with a rotating device and this was employed to study the EDAD technology. The machinability of the mold steel HPM50 and tungsten carbide P20 was investigated by the combined technologies of EDAD. The machined surfaces of these materials were examined by scanning electron microscopy (SEM) and their surface roughness measured by a profilemeter. From the experimental results, it was found that the EDAD machining efficiency was three to seven times than that of normal EDM operation for mold steel. However, the efficiency improvement is hardly detectable for tungsten carbide. In addition, the surface roughness of both materials could be improved in comparison with that achieved after EDM.     

研磨压力对固结聚集体磨料垫自修正影响

固结磨料研磨过程中磨料的微破碎是实现固结磨料垫自修正特性的主要途径,研磨压力是影响磨粒微破碎的关键参数。选用单晶金刚石和聚集体金刚石作为磨粒制备固结磨料垫,在15 kPa压力下以石英玻璃为加工对象进行研磨实验,比较两者的材料去除率及加工稳定性;制备了4种陶瓷结合剂含量的聚集体金刚石,并制备成固结聚集体金刚石磨料垫,探索了不同压力下的固结聚集体金刚石磨料垫的自修正性能;分析了研磨后的工件表面粗糙度和表面微观形貌。结果表明:采用固结聚集体金刚石磨料垫,研磨后工件表面粗糙度低,去除效率稳定;在15~21 kPa的压力下,结合剂含量次高的聚集体金刚石研磨效率高,材料去除率达到8.94~12.43μm/min,加工性能较稳定,研磨后的工件表面粗糙度R a在60 nm左右;在3.5~7 kPa压力下,结合剂含量次低的聚集体金刚石研磨性能较稳定,材料去除率在2.67~3.12μm/min,研磨后的表面粗糙度R a在40 nm左右。高结合剂含量的聚集体金刚石磨粒更适合高研磨压力条件,而低结合剂的聚集体金刚石磨粒更适合于低研磨压力。     

旋转磁场在微小工件磁力研磨加工中的应用

微小工件在工业产品中的应用日益增多,相对于其他工件的加工,微小工件由于在加工过程中装夹困难,至今缺少高效的加工手段。磁力研磨加工中使用旋转磁场被认为是解决微小工件加工困难的有效手段。介绍了磁力研磨技术在应用领域的最新成果,总结了产生旋转磁场几种的方法,分析了磁力研磨加工的加工原理和技术特点。讨论了影响磁力研磨加工质量的几个因素,解释了影响因素的作用原理。最后指出了在磁力研磨加工存在的问题,展望了旋转磁场在微小工件磁力研磨加工中的发展前景。     

Effect of working gap and circumferential speed on the performance of magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is one of the advanced finishing processes in which workpiece is kept between two magnets, and cutting force is controlled by working gap and magnetic field between the two magnets. MAF setup is designed for finishing cylindrical workpieces and it is mounted on lathe machine. The loosely bounded powder is prepared for experimentation by homogeneous mixing of magnetic powder (Fe powder of 300 mesh size (51.4 μm)), abrasive powder (Al₂O₃ of 600 mesh size (25.7 μm), and lubricant called servospin-12 oil. To investigate the effects of working gap and circumferential speed on material removal, change in surface finish and percent improvement in surface finish, a series of experiments have been conducted using in-house fabricated setup. Based upon the results, in general, material removal decreases by increasing working gap or decreasing circumferential speed of the workpiece. Change in surface finish increases by increasing circumferential speed of the workpiece.     

三乙醇胺浓度对固结磨料研磨垫自锐性能的影响

采用不同浓度的三乙醇胺研磨液研磨石英晶体,基于研磨垫磨损率和工件与研磨垫的磨损比,分析了三乙醇胺浓度对石英晶体的去除率及其去除稳定性、研磨垫磨损率、磨损比、研磨摩擦系数、声发射信号和研磨后表面质量的影响。结果表明:随着三乙醇胺浓度的增加,工件与研磨垫磨损比先增大后减小,石英晶体的材料去除率和去除稳定性也对应地先增大后减小,摩擦系数先减小后增大,声发射信号先增加后减小,研磨后工件表面质量先变好后变差。当三乙醇胺浓度为5%时,石英晶体的材料去除率最大,去除率随时间变化最稳定,研磨垫使用寿命最长,表面质量最好。结果表明:研磨液中添加适量的三乙醇胺,会稳定石英晶体加工过程,延长研磨垫使用寿命,提高工件表面质量,降低生产成本。     

The implementation of optimum MRR on digital PC-based lathe system

Optimizing the profit of an individual cutting tool is crucial to the computer numerically controlled (CNC) machining industry. In this paper, the mathematical modeling, the dynamic solution, and the decision criteria through calculus of variations are introduced to achieve the optimal material removal rate (MRR) control of a cutting tool under the fixed tool life. To realize the optimum MRR, a commercialized lathe system with a digital processor controller (DSP) and a man-machine interface is developed. Additionally, the implementation of dynamic MRR control for a real-world industrial case is experimentally performed on our proposed digital PC-based lathe system. It is found that the surface roughness (R _a ) of all machined work-pieces not only stabilizes as the tool consumed, but also accomplishes the recognized standard for finish turning. In this study, the adaptability of the dynamic control of optimum MRR as well as the realization of the digital PC-based lathe system are absolutely guaranteed.     

An experimental study on the effect of magnetic field orientations and electrolyte concentrations on ECDM milling performance of glass

In this work, effects of magnetic field orientation, machining voltage and electrolyte concentration on electrochemical discharge machining (ECDM) performance have been studied. The microchannels have been machined on the glass substrate; microchannel's depth and surface quality have been taken as indexes of machining characteristic. Experimental results show that the Lorenz force of magnetic field affects a direction of bubble's motion, consequently, changes the electrochemical discharge behavior of electrolyte. The presence of magnetic field causes magnetohydrodynamic (MHD) convection which, by its turn, accelerates the repulsion of the bubbles from the cathodic surface. However, it should mention that the direction of bubble movement depends on the magnetic field orientation. If the magnetic field orientation induces upward Lorenz force (downward Lorenz force), the gas bubbles will repel from (will attract to) inter-electrode area. The obtained results demonstrate that when the magnetic field applies, the machined surface will be smoother for the lower concentration values of electrolyte and higher machining voltages. Enhancements of both the machining voltage and electrolyte concentration increase the machining depth. For the same values of applied voltages, application of magnetic field will also increase the machining depth in a certain machining process duration; this will be intensified for the lower values of electrolyte concentration. The results of this study explain how the combination of the magnetic field orientation and the values of machining voltage and electrolyte concentration should be defined in order to increase both the channel depth and surface quality.     

Investigating material removal rate and surface roughness using multi-objective optimization for focused ion beam (FIB) micro-milling of cemented carbide

Cemented carbide has been investigated as a useful material for the fabrication of micro devices. Focused ion beam (FIB) micro-milling has been found to be one of the most appropriate methods for the fabrication of micro devices. The experimental FIB micro-milling on cemented carbide have been conducted according to the L₁₆ orthogonal array of Taguchi technique. Beam current, extraction voltage, angle of beam incidence, dwell time and percentage overlap between beam diameters have been considered as process variables of FIB micro-milling in experimental design. Material removal rate (MRR) and surface roughness have been determined experimentally for FIB micro-milling of cemented carbide and beam current has been identified as the most significant parameter. The minimum surface roughness of 5.6 nm has been reported on cemented carbide, which is not a usual practice to achieve on such polycrystalline material, and hence it may be considered as a significant research contribution. Maximum MRR of 0.4836 μm³/s has been reported. Moreover, genetic algorithm toolbox of MATLAB has been utilized for multi-objective optimization between MRR and surface roughness. The corresponding optimum values of MRR and surface roughness for multi-objective optimization have been represented by pareto optimum solution generated by genetic algorithm. The research work presented in this paper determines the setting of process parameters of FIB micro-milling for achieving a specific combination of MRR and surface roughness on cemented carbide.     

Effects of process parameters on surface roughness in abrasive waterjet cutting of aluminium

Abrasive waterjet cutting is a novel machining process capable of processing wide range of hard-to-cut materials. Surface roughness of machined parts is one of the major machining characteristics that play an important role in determining the quality of engineering components. This paper shows the influence of process parameters on surface roughness (R_a) which is an important cutting performance measure in abrasive waterjet cutting of aluminium. Taguchi’s design of experiments was carried out in order to collect surface roughness values. Experiments were conducted in varying water pressure, nozzle traverse speed, abrasive mass flow rate and standoff distance for cutting aluminium using abrasive waterjet cutting process. The effects of these parameters on surface roughness have been studied based on the experimental results.     

Effect of reciprocating wire slurry sawing on surface quality and mechanical strength of as-cut solar silicon wafers

This paper investigates reciprocating wire slurry sawing for photovoltaic (PV) silicon wafering and compares the resulting wafer surface quality and its mechanical strength to that obtained in unidirectional wire sawing. It is found that wire reciprocation creates two significantly different morphological or cutting zones on the wafer surface. The zone width varies with the distance travelled by the wires, the cutting location on the wafer surface, and direction of wire motion. The size of the morphological zone created during forward motion of the wire is larger than that created during its backward motion. The zone width is found to decrease along the wire cut direction. In addition, there appears to be greater kerf loss and increased surface roughness in the forward cutting zone. In general, results suggest a higher material removal rate during forward motion of the wire than during backward motion. Notwithstanding the surface morphology variations, the fracture strengths of reciprocating wire sawn wafers are found to be quite similar to that exhibited by wafers produced by unidirectional wire sawing.     

Research on chemo-mechanical grinding of large size quartz glass substrate

Finishing process of quartz glass substrate is meeting great challenges to fulfill the requirements of photomask for photolithography applications. For the final finishing of the substrate surface, chemical mechanical polishing (CMP) is often utilized. Those free abrasive processes are able to offer a great surface roughness, but sacrifice profile accuracy. On the other hand, the fixed abrasive process or grinding is known as a promising solution to improve accuracy of profile geometry, but always introduces damaged layer. Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of fixed abrasive machining and CMP. In order to simultaneously achieve high surface quality and high profile accuracy, CMG process has been applied into machining of large size quartz glass substrates for photomask use. Reported in this paper are CMG performances in finishing of quartz glass substrates including material removal rate (MRR), surface roughness, flatness and optical characteristics.     

磨料射流抛光中各工艺参数对材料去除率及抛光区形貌的影响

介绍了磨料射流抛光的工作原理,并从试验出发,针对射流抛光技术的主要工艺参数(入射角度、射流速度、入射距离、抛光液浓度和工作时间等)对抛光特性的影响进行了试验研究.分析了各工艺参数与抛光效率和抛光点形貌的影响关系,从而获得了最佳工艺参数.在此基础上,对一平面K9光学玻璃进行了抛光试验,抛光速率约为30nm/min,抛光区粗糙度小于2.5nm.研究结果为磨料射流抛光加工的进一步研究提供了一定的帮助.     

Influence of reinforcement and lubrication on abrasive wear performance of polyamide

This paper presents the results of studies on the wear performance of various composites of polyamide (nylon 6,6) reinforced with short carbon fibres and lubricated with a solid lubricant, PTFE, under adverse sliding conditions (abrasive wear). The effects of increasing amounts of fillers, fibre orientation, and experimental parameters such as load, and abrading particle size were investigated. The studies revealed that fillers that are very much suitable for adhesive wear applications are detrimental for the abrasive wear mode. Moreover, wear performance showed deterioration with increasing amount of filler concentration. The combination of heterogeneous fillers proved to be detrimental for wear performance. Efforts were made to correlate these investigations with appropriate mechanical properties. It was found that wear performance was greatly influenced by selected experimental parameters. Worn surfaces were examined with SEM to have better insight of the wear mechanism.     

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151 μm (D151), 91 μm (D91) and 46 μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.